The influence of weld defect on the continuous low cycle fatigue property for Type 316LN stainless steel base metal and weldment was investigated with a strain rate of 4×10-3/sec in air atmosphere. Low cycle fatigue tests were conducted at temperature of 823K and 873K. Total strain amplitude was controlled to be 0.4-0.6%.
The 308L stainless steel was used as the welding rod. The welding was done by the GTAW process with the welding direction perpendicular to the rolling direction of the base metal.
The microstructures of the base metal and weldment are γ phase and γ/δ-ferrite, respectively.
The fatigue lives of the base metal had twice longer than those of weldment having no visible defect. From the tensile result, the uniform elongation of the base metal had twice higher than that of the weldment.
For the base metal and HAZ, the faigue lives at the same condition were reliable. But some results of the fatgue lives in the weldment had the lowest fatigue life at the same condition. From the observation of the fracture surface after fatigue tests, there were porosities and internal defects. For weldments having many voids and internal defects, the fatigue lives decreased 50% and 60-70%, respectivly. From the observation of the microstructure near the internal crack, the internal weld defects were existed at the interface among the dendrites grown along the different direction.
